Re: [virtio-dev] Zerocopy VM-to-VM networking using virtio-net

[Jan Kiszka <jan.kiszka@siemens.com>]

Am 2015-04-27 um 16:36 schrieb Luke Gorrie:
> On 27 April 2015 at 16:30, Jan Kiszka <jan.kiszka@siemens.com> wrote:
> 
>> Today, we have posted interrupts to avoid the vm-exit on the target CPU,
>> but there is nothing yet (to my best knowledge) to avoid the exit on the
>> sender side (unless we ignore security). That's the same problem with
>> intra-guest IPIs, BTW.
>>
>> For throughput and given NAPI patterns, that's probably not an issue as
>> you noted. It may be for latency, though, when almost every cycle counts.
>>
> 
> Poll-mode networking applications (DPDK, Snabb Switch, etc) are typically
> busy-looping to poll the vring. They may have a very short usleep() between
> checks to save power but they don't wait on their eventfd. So for those
> particular applications latency is on the order of tens of microseconds
> even without guest exits.

That's one side, don't forget the others (the "normal" guests).

Jan

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